The present invention relates generally to transmissions and more particularly to improved transmissions having split planetary gear assemblies with load sharing and anti-phase technology.
Automobile manufacturers continuously seek to improve performance and reduce weight of vehicles through innovative design and technology implementation. One key area for such improvement is the powertrain, including transmissions and transfer cases. Automobile manufacturers seek to improve the noise, vibration and harshness (NVH) characteristics of a vehicle powertrain to improve overall occupant comfort. Additionally, improvements in size and weight of powertrain components is desired to decrease cost, increase fuel efficiency and provide better packaging underneath a vehicle.
Vehicle transmissions selectively transfer the power and rotational motion of an engine output through varying gear ratios. As such, speed and power to a vehicle driveline can be controlled by each of the gear ratios. As is known in the art, planetary gear assemblies can be interconnected in such a manner as to enable selection of one of a plurality of drive ratios. Planetary gear type-transmissions are available in both manual and automatic varieties. An example of such a planetary-type transmission is shown in commonly-owned U.S. Pat. No. 5,593,358.
Many light-duty trucks and sport-utility vehicles are equipped with a transfer case for providing a four-wheel drive mode of operation. To accommodate differing road surfaces and conditions, many transfer cases are equipped with a gear reduction unit that can be selectively shifted by the vehicle operator to establish high-range (i.e., direct drive) and low-range (i.e., reduced ratio drive) four-wheel drive modes. While layshaft-type gear reduction units are available, most transfer cases are now equipped with a planetary-type gear reduction unit due to improved efficiency and reduced size requirements. An example of such a planetary-type reduction unit installed in a four-wheel drive transfer case is shown in commonly-owned U.S. Pat. No. 4,770,280.
Due to inherent noise associated with spur gears, many planetary-type gear assemblies utilize helical gearing to provide quieter operation. However, a recognized design constraint associated with helical planetary gearsets is the opposing lateral thrust loads generated by the helix angle of the sun gear and ring gear that must be contained. Moreover, it is desirable to allow the helical gearing to be self-centering for optimized sharing of the gear loads which may result in further improvements in durability and noise reduction. In the gear industry, it is known that herringbone gears can be used to address the thrust loading associated with conventional helical gearing. Herringbone gears, however, are difficult and costly to manufacture and, as such, have limited application to vehicular drivetrain products. As such, a need exists to develop planetary gear assemblies which advance the art and address the shortcomings of conventional planetary gear assemblies implemented in vehicle transmission.
It is an object of the present invention to improve the NVH characteristics of planetary-type vehicle transmissions. It is another object of the present invention to reduce the size and weight of planetary-type vehicle transmissions.
It is yet a further object of the present invention to provide an improved gear reduction unit for use with electric or hybrid vehicles.
In achieving the above described objects, the present invention is directed to a split planetary gear assembly having a pair of helical gearsets. The first helical gearset includes a first sun gear, a first ring gear, and a set of first planet gears meshed with the first sun gear and the first ring gear. The second helical gearset includes a second sun gear, a second ring gear, and a set of second planet gears meshed with the second sun gear and the second ring gear. The components of the second helical gearset have the same number of teeth, helix angle, and tooth pitch as the components of the first helical gearset with the exceptions that their angular helix orientation is reversed and they are circumferentially indexed by one-half tooth pitch. In addition, the first and second planet gears are arranged in paired sets and supported on a common pinion shaft which, in turn, is fixed to a planet carrier. The second sun gear is splined for common rotation with and limited axial movement relative to the first sun gear.
In a preferred arrangement, the first and second helical gearsets are juxtapositioned with the first and second ring gears non-rotatably fixed to a stationary housing and rotary power being supplied from an input member to the first sun gear. A clutch sleeve is splined to an output member and is axially moveable thereon between a first position and a second position. With the clutch sleeve in its first position, it couples the output member to the second sun gear for establishing a first drive connection with the input member. With the clutch sleeve in its second position, it couples the output member to the planet carrier for establishing a second drive connection with the input member.
In accordance with a first preferred embodiment of the present invention, at least one split planetary gear assembly is installed in a transmission to provide a plurality of forward drive ratios and a reverse ratio.